1. Field of the Invention
The present invention relates to a unit for imparting lubricity to the surface of an electrophotographic photographic photoconductor for use in an image formation apparatus such as facsimile apparatus, printers, electrophotographic copying machines or the like, which is hereinafter referred to as a lubricity-imparting unit. The present invention also relates to an image formation apparatus using the lubricity-imparting unit and also to an image formation method using the image formation apparatus.
2. Discussion of Background
In the image formation apparatus such as printers, electrophotographic copying machines and facsimile apparatus, using electrophotography, there are disposed various units such as a charging unit, an exposure unit, a development unit, an image fixing unit, a cleaning unit, a charge quenching unit around a photoconductor, representative examples of which are a selenium photoconductor, a silicone photoconductor and an organic photoconductor, and image formation is carried out with successive operation of the above-mentioned units.
In the course of image formation steps, contaminating materials such as ozone and nitrogen oxides are produced in a charging step (hereinafter referred to as corona charge products) and deposited on the surface of the photoconductor, and residual toner components remain on the surface of the photoconductor after a development step. Furthermore, paper dust formed from image transfer sheets in an image transfer step, shavings of a photoconductive layer of the photoconductor, and gas components generated from the image fixing unit are also deposited on the surface of the photoconductor.
When the photoconductor is used for image formation repeatedly for an extended period of time, the above-mentioned contaminating materials build up on the surface of the photoconductor, and the surface of the photoconductor conductor becomes difficult to clean so that the cleaning performance of the photoconductor is reduced, and the abrasion of the surface of the photoconductor is promoted, with an increase in the coefficient of friction of the surface of the photoconductor. Eventually it may occur that a portion of the photoconductor with which a cleaning blade comes into contact is deformed or distorted.
The result is that improper image transfer locally takes place, the quality of images is lowered with considerable insufficiency in resolution and sharpness and the life of the photoconductor is shortened.
A corona charging method and a contact charging method are currently used in practice to charge the photoconductor. The corona charging method in fact produces a much larger quantity of corona charge products than the contact charging method does. Regardless of the quantity of the corona charge products produced, the above-mentioned problems are equally caused once the produced corona charge products build up.
Furthermore, when the coefficient of friction of the surface of the photoconductor is increased by the presence of the contaminating materials and accordingly the frictional resistance of the surface of the photoconductor is increased, the frictional pressure of the cleaning blade applied to the surface of the photoconductor is also increased. The result is that the photoconductor is caused to vibrate and makes discontinuous sharp noise called xe2x80x9cblade""s weepingxe2x80x9d. When this inappropriate state continues and develops, the blade is caught by the photoconductor during its rotation, and eventually the photoconductor is locked and the rotation thereof is stopped, so that the photoconductive layer of the photoconductor is further abraded.
However, the formation of such contaminating materials is unavoidable when the electrophotographic image formation process is carried out.
Generally, photoconductors for use in an electrophotographic image formation apparatus originally have a high coefficient of friction, in particular, when they have not been used yet and brand-new. Therefore, if image formation is repeated without taking any step for reducing the coefficient of friction of such a brand-new photoconductor, the above-mentioned contaminating materials further increase the coefficient of friction of the surface of the photoconductor and inevitably bring about the above-mentioned problems.
Therefore it is desired that there come out a technique that makes it possible to change the surface of the photoconductor to such a surface that the above-mentioned contaminating materials can be easily eliminated therefrom, and are difficult to be deposited thereon.
As one of such techniques, there has been proposed a method of coating a lubricant on the surface of the photoconductor to reduce the coefficient of friction of the surface of the photoconductor and also to improve the abrasive resistance of the surface of the photoconductor.
For instance, in Japanese Laid-Open Patent Application 56-113183, there is proposed a method of continuously applying a lubricant to the surface of the photoconductor by rotating a pouch made of a porous cloth in which a powder-like lubricant is contained or on an external surface for which the powder-like lubricant is deposited, in contact with the surface of the photoconductor, whereby the frictional resistance between the blade and the surface of the photoconductor is reduced.
When the powder-like lubricant is applied from such a rotating member as mentioned above, it is very likely that the powder-like lubricant is scattered to pollute the neighboring place of the photoconductor. Furthermore, it is very difficult to control the amount of the powder-like like lubricant to coat. It is also difficult to reduce the coefficient of friction of the surface of the photoconductor by merely coating the powder-like lubricant thereon, so that it is necessary to form a thin layer of the lubricant on the surface of the photo-conductor. However, when the coated amount varies, the coefficient of friction of the surface of the photoconductor also varies from place to place, so that the desired effect is difficult to obtain.
In Japanese Laid-Open Patent Application 3-269478, there is proposed a method of coating a lubricant which can be formed into a thin layer, such as magnesium silicate or zinc stearate, in the form of a thin layer on a top portion of the cleaning blade in order to prevent the blade from chattering or being turned over or torn up.
This method is effective. However, if the lubricant is not supplied to the coated layer for a long period of time while in use, the lubricating effect of the coated layer will not last. Once the frictional resistance between the cleaning blade and the surface of the photoconductor is increased, a noise with high frequency is generated, and eventually it becomes highly possible that the desired operation cannot be continued any longer. In particular, when a photoconductor composed of a resin for which coefficient of friction increases is used, the above-mentioned noise with high frequency is apt to be generated, so that it may occur the rotation of the photoconductor is stopped and the image formation apparatus is damaged.
In Japanese Laid-Open Patent Application 8-202226, there is proposed an image formation apparatus provided with a cleaning section in which there is disposed a device for applying a lubricant to a brush and then applying a controlled amount of the lubricant from the brush to the surface of the photoconductor.
In Japanese Laid-Open Patent Application No. 8-3052233, there is proposed an image formation apparatus provided with a control unit for detecting a toner image formed on an image bearing member and for coating a lubricant on the surface of the image bearing member in accordance with a reference value for the detection.
Furthermore, in Japanese Laid-Open Patent Application No. 6-342236, there is proposed an image formation apparatus provided with a unit for applying a lubricant to a charging roller for which line speed is made different from the rotation speed of the photoconductor, and for applying the lubricant to the photoconductor via the charging roller. This image formation apparatus is directed to the achievement of the uniform coating of the lubricant by changing the above-mentioned line speed of the charging roller.
The above-mentioned conventional problems, however, have not yet been sufficiently solved even by the above-mentioned proposals.
One of the reasons for this is that the above proposed lubricant coating methods themselves cause the above-mentioned problems. In the above proposals, it is tried to form a uniform coating layer of the lubricant by controlling the coating amount of the lubricant. However the results are not satisfactory since a uniform, thin coating layer of the lubricant is not obtained in the entire image formation area of the photoconductor by the above proposed methods. The thicker the coating layer of the lubricant, the more the coating layer catches the contaminating materials and the more slippery the coating layer becomes, so that there occurs the problem that the cleaning blade does not perform its cleaning function properly.
Even if the lubricant is coated on the surface of the photoconductor, a large number of copies will have to be made by the image formation apparatus before the coefficient of friction of the surface of the photo-conductor reaches a desired low value, and even when the coefficient of friction reaches the desired value, the value is changed as the number of copies made is increased. Thus, this method is not suitable for obtaining any of an immediate effect and a continued effect, so that the desired object cannot be attained by this method.
In addition to the problem concerning the coating method of the lubricant, the lubricant itself has a problem. In the above proposals, zinc stearate is mainly used as the lubricant. As a matter of fact, zinc stearate has excellent lubricity and therefore is suitable for obtaining abrasion resistance. However, zinc stearate has excessively high adherability to the surface of the photoconductor, so that, for example, once zinc stearate adheres to the surface of the photoconductor, the zinc stearate takes in the corona charge products and toner particles, and such materials eventually build in the zinc stearate. As a result, not only a significant reduction in the scraping effect of the cleaning blade, but also a significant local reduction in image quality is caused, and uniform coating of zinc stearate is also hindered.
In short, there has not yet been proposed a method of coating the lubricant on the surface of the photoconductor, which is capable of forming a uniform and thin coating layer of the lubricant on the surface of the photoconductor which is also capable of reducing the coefficient of friction of the surface of the photoconductor immediately after the coating, that is, when about 50 to 100 copies have been made with image formation after the coating layer is formed, and which is capable of maintaining the reduced coefficient of friction without any change even when the image formation is performed repeatedly by making a number of copies.
It is therefore a first object of the present invention to provide a lubricity-imparting unit for imparting lubricity to the surface of an electrophotographic photoconductor by coating a lubricant on the surface thereof in order to obtain excellent image quality in a stable manner even when the electrophotographic photoconductor is used repeatedly for image formation for an extended period of time, which lubricity-imparting unit is also capable of coating a uniform and thin layer of the lubricant on the surface of the photoconductor, with an immediate effect for reducing the coefficient of friction of the surface of the photoconductor, and also with a continued effect of maintaining the reduced coefficient of friction, and which lubricity-imparting unit is also capable of reducing the coefficient of friction of the surface of the photoconductor, without generating abnormal noise such as the noise called xe2x80x9cblade""s weepingxe2x80x9d during the formation of images.
A second object of the present invention is to provide an image formation apparatus using the above-mentioned lubricity-imparting unit.
A third object of the present invention is to provide a method of image formation, using the above-mentioned image formation apparatus in which the above-mentioned lubricity-imparting unit is employed.
The first object of the present invention can be achieved by a lubricity-imparting unit which imparts lubricity to a surface of an electrophotographic photoconductor by being disposed in contact with the surface of the electrophotographic photoconductor, at least a surface of the lubricity-imparting unit which comes into contact with the surface of the electrophotographic photoconductor comprising a flexible lubricating material and having a length at least capable of covering an image formation region of the electrophotographic photoconductor lengthwise.
In the above lubricity-imparting unit of the present invention, the flexible lubricating material may be either a film-shaped material or an elastic structure.
The lubricity-imparting unit of the present invention may further comprise an elastic member which is built in the flexible lubricating material.
It is preferable that the flexible lubricating material comprise a fluoroplastic.
It is also preferable that the flexible lubricating material have a thickness of 50 to 500 xcexcm.
The lubricity-imparting unit may further comprise an elastic member which is built in the lubricity-imparting unit, with the lubricity-imparting unit having such a structure that is fixed to a support, optionally with the lubricity-imparting unit further being held between the support and a holding plate.
In the lubricity-imparting unit of the present invention, it is preferable that a portion of the flexible lubricating material, which comes into contact with the surface of the electrophotographic photoconductor, be lined with a liner,
In the lubricity-imparting unit of the present invention, a portion of the flexible lubricating material, which comes into contact with the surface of the electrophotographic photoconductor, may be marked on an inside of the portion with a marker for judging an abraded state of the flexible lubricating material.
The second object of the present invention can be achieved by an electrophotographic image formation apparatus comprising (a) an electrophotographic photoconductor, (b) a charging unit, (c) an exposure unit, (d) a development unit, an image transfer unit, and (e) a cleaning unit which are disposed around the electrophotographic photoconductor, and (f) a lubricity-imparting unit which imparts lubricity to a surface of the electrophotographic photoconductor by being disposed in contact with the surface of the electrophotographic photo-conductor, at least a surface of the lubricity-imparting unit which comes into contact with the surface of the electrophotographic photoconductor comprising a flexible lubricating material, and having a length at least capable of covering an image formation region of the electrophotographic photoconductor lengthwise.
In the above electrophotographic image formation apparatus, the flexible lubricating material may be either a film-shaped material or an elastic structure.
In the electrophotographic image formation apparatus, an elastic member may be built in the flexible lubricating material.
It is preferable that the flexible lubricating material comprise a fluoroplastic.
It is also preferable that the flexible lubricating material have a thickness of 50 to 500 xcexcm.
In the electrophotographic image formation apparatus, an elastic member may be built in the lubricity-imparting unit, with the lubricity-imparting unit having such a structure that is fixed to a support, optionally with the lubricity-imparting unit further being held between the support and a holding plate.
Furthermore, in the electrophotographic image formation apparatus, it is preferable that a portion of the flexible lubricating material, which comes into contact with the surface of the electrophotographic photoconductor, be lined with a liner.
In the electrophotographic image formation apparatus, a portion of the flexible lubricating material, which comes into contact with the surface of the electrophotographic photoconductor, may be marked on an inside of the portion with a marker for judging an abraded state of the flexible lubricating material.
In the electrophotographic image formation apparatus, it is preferable that the lubricity-imparting unit be disposed between the cleaning unit and the charging unit.
In the electrophotographic image formation apparatus, an auxiliary cleaning unit may be disposed between the lubricity-imparting unit and the cleaning unit.
The third object of the present invention can be achieved by an image formation method of forming images, using an electrophotographic image formation apparatus comprising (a) an electrophotographic photoconductor, (b) a charging unit, (c) an exposure unit, (d) a development unit, an image transfer unit, and (e) a cleaning unit which are disposed around the electrophotographic photoconductor, and (f) a lubricity-imparting unit which imparts lubricity to a surface of the electrophotographic photoconductor by being disposed in contact with the surface of the electrophotographic photo-conductor, at least a surface of the lubricity-Imparting unit which comes into contact with the surface of the electrophotographic photoconductor comprising a flexible lubricating material, and having a length at least capable of covering an image formation region of the electrophotographic photoconductor lengthwise, wherein an image is formed with the lubricity-imparting unit being constantly set in contact with the surface of the electrophotographic photoconductor or being intermittently brought into contact with the surface of the electrophotographic photoconductor.
In the above image formation method, it is preferable that the lubricity-imparting unit in contact with the surface of the electrophotographic photoconductor form a nip of 0.2 mm or more therebetween.
In the image formation method of the present invention, it is preferable that the surface of the electrophotographic photoconductor have a coefficient of friction of 0.4 or less when the lubricity-imparting unit comes into contact with the surface of the electrophotographic photoconductor or after the image has been formed. It is also preferable that in the image formation method of the present invention, the cleaning unit comprise a cleaning blade for cleaning the surface of the electrophotographic photoconductor, and a lubricant be coated on at least one portion of (1) a top end portion of the cleaning blade, (2) a portion around the top end portion of the cleaning blade, or (3) a portion of the surface of the electrophotographic photoconductor near the cleaning blade, before the electrophotographic image formation apparatus is initiated to be brought into operation for forming the image.